Justin was definitely being held back by *NSYNC. Although he wrote and produced several songs on Celebrity it was still w/in a box.

Justified was released a year and a half after Celebrity and showcased so much more of Justin's talent.

Vocally, Justin is amazing and we only got to see once facet of Justin's voice in *NSYNC (similar to how he sings in Never Again). But he has so much more range from Love Don't Love Me to Damn Girl to What Goes Around Comes Around to Let's Take A Ride to Nothing Else to Sexy Back.

Furthermore, I think he was limited with his subject matter. (As was JC).